Misfiring 1300 Beetle when cold

[weltmeister72]

Hi folks, I’m hoping you can help because I’m just about at my wits end trying to solve this problem. My car is a standard 1972 1300 Beetle, running electronic ignition.

Sorry it’s a long one…

Initial Symptom:

Beetle starts fine from cold. Misfires badly over first few miles of any drive, violently jerking. Once the engine warms up it disappears and Beetle will drive nicely for hundreds of miles. However, once switched off it becomes a pain to restart. Will usually only restart with foot to floor on accelerator.

Upon removing spark plugs they were badly fouled up.

Work done so far (I changed one thing at a time and re-tested, same problem).

- Changed spark plugs with new correctly gapped ones
- Changed HT leads for new double silicone ones
- Swapped coil for known good
- Swapped distributor over (Petronix, electronic)
- Re-set timing
- Checked choke operating correctly
- Sprayed duck oil around carb gasket and manifold boots to check for vacuum leak. Can’t see any bubbling or duck oil being drawn in.
- Compression tested (all good)
- Adjusted fuel mixture (leaner/richer)
- Replaced perishing flexi fuel lines at rear of car
- Ensured fresh E5 petrol (has done this on different petrol types from different suppliers - not a fuel issue)
- Checked air filter

None of the above solved the problem. Car idles sweetly and revs freely without issue when sitting still.

I then put it into an old school VW specialist who did the following:

- Checked and adjusted valve clearances
- Fitted refurb carb (Solex 31 PICT 3, which I supplied)
- Changed plugs again
- Re-timed
- Set fuel mixture

Despite this the initial symptom persists. The car is actually worse now with the new carburettor on it as it’s completely bogged down when trying to accelerate, especially at lower rpm. Pulling away from slow corners is really problematic. I took car straight back explaining the problems. Garage insinuated I wasn’t driving the car correctly and I need to drive it hard, which irritated me. Garage is quite some distance away from where I live so I just drove the car home.

When not under load car will bumble along fine. It now restarts much easier than before.

I played with timing, a little at a time and it didn’t solve the bogging down. I am hopeful adjusting fuel mixture a little will solve the bogging down, but that still leaves the initial symptom.

Has anyone else experienced this? It’s driving me nuts and I’m getting to the stage of just parking it up for the season. Which is frustrating as I love this car. I’ve no more money to throw at it just now.

[VW_Jimbo]

Cap and rotor?

I had a rotor partially burn through to the distributor shaft. It would run great every other time. Some days it was really hard to start and other days, just fine. Then it started to intermittently miss at higher rpms, but randomly. Took me a few months to track it down to the rotor. Even when I was convinced it was the rotor, I was still scratching my head. There was no visual clue.

I finally drove it till it would not start anymore, but thankfully I had a full set of ignition parts with me! I opened up the cap , pulled off the rotor and found this!

See that black spec with a white dot in it? Up were the key is cast into the rotor? That’s where it burned through!

Worth a good look! Good luck!
_________________
Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[heimlich]

That's neat. Just goes to show electricity will go anywhere you let it.
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[weltmeister72]

[wcfvw69]

How old is your fuel pump? If it's on it's last legs, it could be pumping enough gas to keep the carb bowl partially full. But, under load, it can't keep up and the engine is starving for fuel.

Your symptoms sound electrical to me.

* Coil
* Condenser or points replacement module
* As mentioned, cap or rotor issue
* A 12 volt wires grounding out on something occasionally

Do you have another know distributor with a good cap/rotor, points and condenser you can try?
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[heimlich]

[baldessariclan]

[weltmeister72]

Thanks for the comments. For the avoidance of doubt, as above, everything within the distributor has already been eliminated as a possible cause. Every consumable part was changed first and then when that didn’t work the full distributor was swapped over.

I am going to try driving it with the fuel filler cap removed, in case the petrol tank is not venting. Then…

My car has a second inline fuel filter within the engine bay. I am going to remove this, and change the inline filter underneath the car.

I shall look at the choke as suggested above. The initial symptom does present when the choke would be in use. However, the symptom has been present with two different carburettors, each with its own auto choke.

[VW_Jimbo]

What do the spark plugs look like?

And what does the engine look like sitting in the car?

My money is on the coil!
_________________
Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[weltmeister72]

Perhaps I’m wasting my time here. Forget it.